Some fungal diseases in humans no longer respond to medicines, which increases the risk of severe illness and death as well disease spread, according to a new report.

On Tuesday, the World Health Organization (WHO) published what it calls its first-ever report on the lack of tests and treatments for fungal infections.

Yeasts, moulds and mushrooms are all examples of fungi. Common toenail infections or vaginal yeast infections are common and treatable, but that's not always the case.

"Fungal diseases are an increasing public health concern, with common infections — such as Candida, which causes oral and vaginal thrush — growing increasingly resistant to treatment," WHO said.

Here are some key things to know about fungal diseases in Canada and around the world.

What are fungal diseases and why do they matter?

Fungal diseases are a type of infectious disease that spread from person to person, like touching someone who has the infection or sharing clothes with them, or in an environment, like from breathing in spores.

Biochemistry professor Gerry Wright says the WHO's reports draw attention to an important problem.

"All of us have someone in our lives that they know how it's been touched by cancer so it makes them vulnerable, or who have had a kidney transplant or a heart transplant or who has lupus," said Wright, who searches for new ways to kill fungal pathogens at McMaster University in Hamilton.

These conditions are all treated with immune-suppressing drugs, he says — and people with weakened immune systems are more susceptible to fungal disease.

Invasive fungal diseases occur when fungi enter blood, tissue and other places in the body that are normally sterile.

For fungi in the WHO's top "critical priority" category, mortality rates reach up to 88 per cent, it said in a release. 

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"You can get lung infections, so fungal pneumonia," Wright said. "There's even certain kinds of fungi that have an affinity for the neurological system so you can get growth in the spinal cord and in the brain. Pretty much anywhere where you can think of would be a bad place for an infectious organism to be, fungi can make their way in there."

What's new?

Better treatments for diseases like cancer mean more people are likely to be living with immunocompromised conditions, which also could mean increases in cases of invasive fungal diseases, the WHO said.

Rebecca Shapiro, an associate professor who studies fungal disease at the University of Guelph, pointed to a few other factors behind the increasing rates.

"We've seen increasing fungal infections, especially there was a lot of co-occurrence of fungal disease during the COVID-19 pandemic," she said, "so people who are very sick and hospitalized with COVID were also really highly susceptible to fungal disease."

While about a dozen classes of antibiotics are available to treat bacterial infections, there are only three main classes of antifungals, she said. 

"We also have to be concerned about how we are using antifungals both in the clinic and actually also in agriculture," Shapiro said.

They're sprayed on crops to prevent mould, blight and rust diseases. 

"One of the issues is there seems to often not be a lot of communication with regards to how drugs are being used on both sides."

Take the Aspergillus genus, for example, whose spores are common in the environment. But the Aspergillus fumigatus species causes a variety of illnesses, from allergic diseases to invasive aspergillosis, a serious fungal infection, depending on a person's immune and lung status. This particular infection is increasingly resistant to antifungals because of use in both the clinic and in agriculture, which the WHO called "worrisome." 

To help combat this, doctors encourage patients to finish the entire course of an antifungal treatment. Properly disposing of medicines also prevents antifungals from entering the environment, where the microbes may also develop resistance. 

What's the situation in Canada?

Candida auris is another fungal pathogen that the WHO called a critical priority. The form of yeast spreads easily in hospitals and long-term care homes, particularly among people with weakened immune systems. It can be hard to treat successfully when it invades the bloodstream and is frequently resistant to antifungal medications.

As of March 26, a total of 65 cases of C. auris have been reported across the country since 2012, when the first case was identified, said the Public Health Agency of Canada. Of those cases, 46 have been identified since 2019.

"C. auris can be multi-drug-resistant, which means it can be unaffected by at least two types of antifungals," the federal agency said in an email. "All known cases in Canada so far have responded to at least one of the recommended treatments."

Most fungal pathogens grow on the skin, which has a cooler temperature than inside the body. 

Wright said C. auris is an exception: "The thought here is that that might be one of the first examples of climate change affecting a pathogenic organism because now it can grow pretty well at human body temperature 37 [C], and so that's now starting to be a big concern."

What's next?

WHO said antifungal medicines that work against a wide range of severe infections are needed, and children are particularly underserved. There aren't enough approved treatments, the organization said. Over the past decade, just four new antifungals have been approved in the U.S., the EU or China. And of the nine currently in clinical development, only three are in the last stage, meaning there are few approvals expected in the next decade.

Currently available medicines can have serious side effects and require prolonged hospital stays, it said. 

Both Wright and Shapiro's labs work to develop potential antifungals.

"There really is a group of people who understand that this is a big problem and are working to try and solve it," Wright said. "But you know, we don't have solutions overnight."